Input validation error in Netty - #VU141319
Published: August 8, 2026
Vulnerability identifier: #VU141319
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass mTLS requirements.
The vulnerability exists due to an incorrect offset check in io.netty.handler.ssl.SslClientHelloHandler#decode when parsing a fragmented TLS ClientHello whose handshake header spans multiple records. A remote attacker can send a specially crafted fragmented TLS ClientHello to bypass mTLS requirements.
This issue affects deployments where per-SNI SslContext selection is the only mTLS gate, the default SslContext is permissive, and no secondary peer-certificate verification exists at the application layer.
Affected software
Netty
Remediation
Install security update from vendor's website.
Netty - addressed in versions 4.1.137, 4.2.17